The present invention relates generally to an improved triple-effect absorption refrigeration system and method, and more particularly to such a system which utilizes three generators with a double-condenser coupling that is provided by coupling the high temperature condenser with both the medium temperature generator and the low temperature generator to provide improved internal heat recovery and thereby increasing the thermal efficiency of the system.
Absorption refrigeration systems which typically utilize hydrocarbon fuels, such as natural gas or oil, as the system-operating heat source have undergone considerable modifications in recent years in order to increase the thermal efficiency or the coefficient of performance (COP) of the system and thereby improving the economics of operating the system on hydrocarbon fuels. The modifications were usually made to the basic commercial absorption refrigeration system which utilizes a single-effect absorption system that typically comprises a desorber or generator, a condenser, an evaporator, and an absorber coupled together. In the single-effect system the working fluid or refrigerant-absorbent solution, commonly known as a solution pair, is heated in the generator by an external heat source, normally the combustion of a hydrocarbon fuel, to vaporize the refrigerant from the solution and concentrate the absorbent liquid. The concentrated absorbent liquid is returned to the absorber while the vaporized refrigerant is condensed to liquid in the condenser and then evaporated in the evaporator to provide the desired refrigeration effect. The COP of a single-effect absorption refrigeration system is typically in the range of about 0.6 to 0.7.
An increase in the COP of absorption refrigeration systems was provided by the development of the double-effect absorption system in which two generators are coupled to the absorber with the second generator being operable at a higher temperature and pressure than the first generator. In this system the high temperature generator is externally heated while the first generator is heated by the heat rejected during the condensation of the vaporized refrigerant from the high temperature generator in the high temperature condenser. This arrangement effectively utilizes the external heat energy in both generators to provide an increase in the COP up to about 1.0 to 1.3.
A modification of the double-effect absorption refrigeration system was provided by the development of the dual-loop absorption system which utilizes two separate but complete refrigeration absorption units or loops operating at different temperatures with at least the condenser in the higher temperature loop being in heat exchange relationship with the generator in the lower temperature loop to provide the source of heat for operating the entire lower temperature loop. Such a dual loop system is described in U.S. Pat. No. 4,542,628 and has a COP approximately the same as that of the double-effect absorption refrigeration system.
A triple-effect absorption refrigeration system as described in U.S. Pat. No. 4,732,008 also combines two single-effect absorption circuits in a manner wherein the components of the system are arranged differently from the dual loop system described above for utilizing the externally applied heat three times to produce the desired cooling effect in the evaporator.
The development of multiple-effect absorption refrigeration systems also includes a triple-effect system wherein three generators and condensers are utilized. The generators are coupled to a single absorber while the condensers are individually coupled to a single evaporator. A typical triple-effect system utilizing such a three generator arrangement is described in U.S. Pat. No. 4,531,374 (FIG. 44G). The three sets of generators and condensers function at different temperatures and pressures. External heat is applied to the high temperature or third generator while heat rejection from the high temperature or third condenser is used to heat the medium temperature or second generator. Also, the heat of condensation from the medium temperature or second condenser is used to heat the low temperature or first generator. The condensed refrigerant from the first, second, and third condensers is evaporated in the evaporator to provide the desired refrigeration effect. The COP for such a triple-effect system is about 1.3 which corresponds to the higher thermal efficiencies provided by the double-effect and dual-loop, double-effect systems described above.